The advantages of providing a liner of friction reducing, wear resistant material on one lip of an oil seal are known in the art. Some of the advantages of lining the lip of an oil seal include improving durability and wear resistance. Another advantage is the reduction of friction between the relatively rotating parts. Suitable liners are made from filled or unfilled polytetrafluoroethylene (PTFE) or other materials. PTFE suitable for oil seals may include fillers such as fiberglass reinforcements and graphite.
Oil seals are generally used between relatively rotatable parts to seal oil or grease in a predetermined location for lubrication. Oil seals include a lip which either rotates relative to a stationary member or is held stationary against a rotating member.
Frequently it is advantageous to provide more than one lip on an oil seal. An auxiliary lip, or excluder lip, may be provided on an oil seal to exclude water or contaminants from the main lip of the seal. Generally oil seals are provided with only one lined lip due to the difficulty and expense of providing more than one lip with a liner. Previously, to provide two lip liners on an oil seal it was necessary to use special molding dies for clamping two Teflon elements in separate locations. According to one approach, the primary lip liner is clamped between the upper and lower dies of the mold and an excluder lip liner is clamped between a detachable core element and the lower die.
It is desirable to provide a PTFE liner on an auxiliary seal lip because auxiliary lips are not lubricated and are subject to rapid wear.
Additional manufacturing steps required to clamp two lip lining blanks in the mold increase the cost of such seals making the cost prohibitive for most seal applications. Moreover, conventional molds required to produce seals having two separately lined lips are expensive and costly to operate.
Providing two blanks increases the amount of lip lining material wasted since the clamped segments of both the primary lip liner and the excluder lip liner are normally trimmed off.